On a Saturday night last September, a crowd of celebrities, Silicon Valley titans, and Hollywood executives gathered at Malibu House for television producer Mark Burnett for a birthday party celebrating venture capitalist Vivi Nevo.

The richest of them was Jeff Bezos, founder of Amazon.com Inc., whose share of Amazon is about $ 125 billion. He sat in the middle of the action and seemed to enjoy the spotlight, said a guest who knew Mr. Bezos.